Over-normalized (loud) sound output in AC3, EAC3 etc and DTS

  • Vouk:

    Output is def over-normalized in Voukoder. I can supply A/B comparisons if nec, but have you not also noticed this. Take in AC3 source file, re-encode as AC3 or EAC3 or DTS or TrueHD and we have noticably louder output in Voukoder encoded files. Not sure why that would be. However if you use SurCode in Premiere, which I would consider a standard, I notice it uses different channel levels for its outputs for AC3 and EAC3. Can you check on this and see if you agree with me.

    • Official Post

    I'm not at home so I can't try it out yet.

    Maybe it has to do with how premiere decompresses the audio signal from ac-3 to float values. I feed them straight away to FFmpeg.

    Need to investigate this more.

    Edit: It has one parameter "Clipping true/false". Currently it is set to false always (as I don't want to cut any peaks - that what expect it is used for).

  • Vouk

    Added the Label In Progress
    • Official Post

    I will deal with this on the weekend.

    Edit: Or even before the weekend ...

    1. Created an audio file with Audacity. First tone is 100%, second is 50% and third is 25% (First two mono tracks)
    2. Adobe AAC created this stereo track. Amplitudes look okay
    3. Voukoder (Connector 1.2.0, Voukoder 3) with AC-3 also created same looking results.

    Can you try to reproduce?

    • Official Post

    So from the encoder and decoder point of view everything looks alright. So no bug in premiere and/or voukoder.

    Ergo: It has to do with how the player plays it and thus it should be the metadata in the encoder settings: https://www.ffmpeg.org/ffmpeg-codecs.html#AC_002d3-Metadata


    -dialnorm value

    Dialogue Normalization. Indicates how far the average dialogue level of the program is below digital 100% full scale (0 dBFS). This parameter determines a level shift during audio reproduction that sets the average volume of the dialogue to a preset level. The goal is to match volume level between program sources. A value of -31dB will result in no volume level change, relative to the source volume, during audio reproduction. Valid values are whole numbers in the range -31 to -1, with -31 being the default.

    Sounds very much like it could be the cause.

    Maybe you can try?

  • you can try yourself, encode at dialnorm -31 or -1. I play back in MPC64 or bitstream to my receiver. Whatever dialnorm value you set in Voukoder it doesn't change the playback volume strangely. So it must be some other bit of metadata.

    • Official Post

    I have to say that I am not an expert in encoder configuration options. I try my best but what I currently do is compare this on a technical, programmers level.

    But what I've also found is:

    • Premiere renders a mono audio track of 100% amplitude to only 70%
    • Stereo is 100%

    I really don't understand this. Why does mono get rendered to 70% only?

    scarbrtj What do you use? Stereo or 5.1?

  • I am using AC3 renders almost exclusively, and 5.1 the majority of time. It will be a 5.1 source that's AC3, or EAC3, and I will render it as EAC3 or AC3 using Vouk. Usually 5.1 sources rendered as 5.1, but sometimes 2.0 sources rendered as 2.0 AC3 or EAC3. Either way, playback is louder than the original. Playback will be either in MPC in Windows, or direct bitstream by a client (usually a Roku or a Shield or occasionally a Windows PC) into an AC3 or EAC3 capable audio receiver or TV. As we have show previously though, the actual "data" of the rendered track is perfect and matches the original in every way. It's some sort of "metadata" that is telling the playback device(s) to boost the audio up. And as I have stated previously, the SurCode software puts out AC3 and EAC3 renders that when played back match the original's loudness characteristics. In Premiere, you generally have to output only in MP4 containers using SurCode.

    The mono issue is weird but I have not done much mono work and have no complaints there (for now lol).

    EDIT: will also add our default -4.5/-6 dB levels for channels in options do not match the default values in SurCode.

  • Vouk

    Set the Label from In Progress to Not a bug
  • I agree with that
    Will you be working on having Voukoder write different metadata settings

    I am not sure this is "essential" but, technically, this is a "non-conforming" output it seems